The Spring of 2020 will be remembered for several reasons. The Covid 19 Pandemic, a 2 month drought and the defoliation of thousands of trees throughout York Region.
The level of the LDD infestation surprised a lot of arboriculture companies this year as the numbers of caterpillars and the cry for help from homeowners was overwhelming. It is the worst outbreak since the late 90’s. Destructive gypsy moth larvae can defoliate a tree in days.
Many millions of gypsy moth (Lymantria dispar dispar, LDD) caterpillars emerged across Ontario, causing ecological concerns from North Bay and Sault Ste. Marie to Windsor, through York Region and out to Ottawa. The species was introduced to eastern North America from Europe in the late 1800’s through a failed attempt to harvest silk from LDD cocoons.
These invasive caterpillars damage native trees and shrubs, destroying habitat and food sources for wildlife by consuming foliage including Oaks – the preferred host plant for LDD. Rural and urban areas are teeming with the caterpillars, which disturb residents with vast quantities of caterpillar feces and by covering external walls with dense infestations as larvae look for sites to turn into moths.
Dan Rowlinson, the Ministry of Natural Resources and Forestry's provincial coordinator for the forest health monitoring program, said he suspects property owners, many working from home during the COVID-19 pandemic, are just more keenly attuned to the health of their trees this year. And, he said in the case of deciduous trees, all hope is not lost. "A defoliated tree is not a dead tree," he said. The problem isn't isolated to rural and remote areas.
LDD has been found on approximately 500 species of trees. LDD are a concern because the larvae feed voraciously, mostly on the leaves of deciduous (leafy) trees, but also on some conifers (evergreens). During the larval stage, a single LDD moth caterpillar can eat an average of one square metre of leaves. Leaves play a major role in food production for trees, converting light into food by photosynthesis. Reducing the leaf surface available to capture sunlight causes a loss in food production. Deciduous trees can sometimes produce a second crop of leaves, but after repeated defoliation, trees may die or become so weakened that they are vulnerable to secondary infestations. Evergreens may die from this defoliation. The discovery of the Asian LDD moth strain in Canada has raised new concerns. The Asian LDD moth prefers coniferous trees, is better adapted to colder climates, and the female is able to fly. These traits make the Asian LDD moth a serious threat to Canadian forests and the urban landscape.
LDD overwinter in the egg stage in a buff-coloured egg mass laid on the tree and covered with a dense patch of hairs. Larvae hatch in late April to early May as Bradford Pear, Redbud and Amelanchier are blooming. Newly hatched larvae produce silk in order to disperse via wind to other hosts. Larval development takes about seven weeks and can be up to 6 cms long. Young larvae are dark with irregular yellow markings on their backs and a black head capsule. As larvae mature (four to six instars), they develop 5 pairs of blue spots and 6 pairs of red spots on their backs. Moths pupate in protected sites, like under loose flaps of bark or on woodpiles. Adults emerge after pupation (about 10-14 days) beginning about mid-July to mate and lay eggs. Females are creamy white with a wingspan of about 2 inches; males are brown with darker bands. Females cannot fly, they attract males with pheromones, mate and lay eggs near the pupation sites. Egg masses are laid in July to August.
References; Government of Canada, Ontario Nature – Noah Cole
SHADY LANE EXPERT TREE CARE CAN HELP REDUCE POPULATIONS.
- Shady Lane can provide treatments that target the Heritage and significant or signature trees on larger properties.
- Shady Lane has certified Arborists that will climb your trees where necessary, to look for and destroy egg masses during the dormant season, well before they hatch in Spring.
- Shady Lane has licensed technicians that will use approved insecticides to manage young larvae as they emerge in the Spring.
- Shady Lane will install pheromone traps in the late summer, at the time of the emergence and flight of adult male LDD, to capture the male moths to further reduce populations.
- LDD have many natural enemies, including predators, parasitoids and pathogens and the NPV (a virus) which may cause a significant drop in populations within a couple of years of an outbreak. These enemies may not reduce populations to a tolerable level during a season of outbreak.
- Property owners can install a folded burlap cloth wrapped around their trees. This provides a daytime shelter for larger larvae or pupae. Homeowners can then collect them from these shelters and destroy them.